In recent years, a projector apparatus for a digital cinema is used in film showing since a high definition image can be offered, and in a projector apparatus for a digital cinema, in order to project a clear image to a large screen, it is necessary to use a high intensity light source. Therefore, a light source apparatus equipped with a short arc type xenon lamp, which emits light of the wavelength near that of sunlight, and whose rated power is about 2-7 kW, is used.
FIG. 8 is a schematic perspective view showing the structure of a conventional light source apparatus. FIG. 9A is an enlarged perspective view of a conventional lamp position adjustment mechanism, and FIG. 9B is an explanatory cross sectional view of a relevant part thereof provided in a conventional light source apparatus. A light source apparatus 60 has a casing 11 which is made up of a casing substrate 111, and a casing cover 112 in which a light emission window 112a is formed in a front side face thereof. In the casing 11, enclosed is a discharge lamp 12 which has an arc tube portion 12a and side tube portions 12b extending from both ends of the arc tube portion 12a, respectively; a back side light condensing reflection mirror 14 which is supported by a reflection mirror support member 13, and which directly reflects visible light emitted from the discharge lamp 12 so as to condense it towards the light emission window 112a; a front side reflection mirror 15 for reflecting back light which is emitted from the discharge lamp 12, but which is not caught by the back side light condensing reflection mirror 14 and is emitted toward the front side, to the back side light condensing reflection mirror 14; and a lamp position adjustment mechanism 16 which holds one of the side tube portions 12b of the discharge lamp 12, and adjusts the position of the discharge lamp 12 in an X axial direction, a Y axial direction, and a Z axial direction.
The discharge lamp 12 comprises the approximately spherical arc tube section 12a and the cylindrical side tube portions 12b which extend from the both ends of the arc tube portion 12a. While a pair of electrodes is arranged so as to face each other inside the arc tube portion 12a, xenon gas is enclosed so that the vapor pressure of the xenon gas at time of lighting may fall within a range of 2 to 8 MPa. Cylindrical mouthpieces 12c for electric supply, each of which is electrically connected to an external lead extending from each end portion of the side tube portions 12b towards the outside, are attached to the respective side tube portions 12b of the discharge lamp 12. One of the mouthpieces 12c has a two-section structure, and is held by a lamp holder 12d which is connected to a lamp connection section 164, and the other side tube portion 12b is not fixed so as to be a free end, whereby the lamp is cantilevered, so that the tube axis of the discharge lamp 12 is held with the posture extending in parallel with the ground (the casing substrate 111). Electric power is supplied to the pair of electrodes arranged in the arc tube portion 12a through the mouthpieces 12c which are attached to the side tube portions 12b of the discharge lamp 12, by a power supply device for lighting (not shown) arranged outside the casing 11, wherein visible light is emitted from electric discharge arc generated by producing dielectric breakdown between the pair of electrodes. The range of such rated lighting electric power of the discharge lamp 12 is 2 to 7 kW.
In the back side light condensing reflection mirror 14, a front opening and a back opening 14a are provided. Also, a spheroidal reflective surface (reflection face) on which light emitted from the discharge lamp 12 is reflected to the light emission window 112a of the casing 11 is formed inside the back side light condensing reflection mirror 14. The spheroidal reflective surface of the back side light condensing reflection mirror 14 are made from a dielectric multilayer which reflects visible light, but transmits ultraviolet radiation and infrared light transmits towards the back side thereof. A front opening and a back opening are provided in the front side reflection mirror 15, and the front side reflection mirror 15 has a spheroidal reflective surface which reflects light emitted from the discharge lamp 12 but which is not be caught by the back side light condensing reflection mirror 14, towards the back side light condensing reflection mirror 14. The back side light condensing reflection mirror 14 and the front side reflection mirror 15 are disposed in a predetermined position in the casing 11 by the reflection mirror support member 13.
As mentioned above, the mouthpiece 12c is attached to the side tube portion 12b of the discharge lamp 12, and the mouthpiece 12c is attached to the lamp holder 12d, after the discharge lamp 12 is inserted in the openings of the front side reflection mirror 15 and the back side light condensing reflection mirror 14 so that the outer circumference of the mouthpiece 12c attached to one of the side tube portions 12b of the discharge lamp 12, may not be in contact with opening end edges of the back side light condensing reflection mirror 14 and the front side reflection mirror 15.
As shown in an FIG. 9A, the lamp position adjustment mechanism 16 includes an X axial direction drive mechanism 161 fixed on the casing substrate 111; a Y axial direction drive mechanism 162 fixed on the X axial direction drive mechanism 161; a Z axial direction drive mechanism 163 built in a drive section 162X of the Y axial direction drive mechanism 162; and the lamp connection section 164 for holding the side tube portion 12b of the discharge lamp 12, which is connected with the Z axial direction drive mechanism 163, through the mouthpiece 12c. 
The X axial direction drive mechanism 161 comprises a pair of rails 161x which face each other, and a drive section 161X which slides in the direction of the X axis in a state where the X axial direction drive mechanism 161 is sandwiched at both ends edges thereof by the pair of rails 161x. The position in the direction of X axis of the discharge lamp 12 is adjusted by applying a driving force to the drive section 161X by a predetermined drive means so that the drive section 161X may slide in the direction of X axis.
Similarly, the Y axial direction drive mechanism 162 comprises a pair of rails 162x which face each other, and a drive section 162X which slides in the direction of the Y axis in a state where the Y axial direction drive mechanism 162 is sandwiched at both ends edges thereof by the pair of rails 162x. The position in the direction of Y axis of the discharge lamp 12 is adjusted by applying a driving force to the drive section 162X by a predetermined drive means so that the drive section 162X may slide in the direction of Y axis.
As shown in FIG. 9B, the Z axial direction drive mechanism 163 comprises a drive gear 163a connected to a drive unit (not shown), a rotational axis section 163b which is connected to the drive gear 163a, and has a screw section 163p, on an upper portion of which a screw processing is carried out, and an arm 163c which has a hole 163q having a bottom, in a base end side on which a screw processing is carried out. The screw section 163p of the rotational axis section 163b is screwed in the hole 163q (having a bottom) of the arm 163c in which a screw processing is carried out. The position in the direction of the Z axis of the discharge lamp 12 is adjusted by applying a driving force to the rotational axis section 163b through the drive gear 163a by a predetermined drive means so that the rotational axis section 163b goes up or down while rotating, whereby the arm 163c which is screwed in the rotational axis section 163b goes up or down. Such a drive means may be either a manual operation or automatic action. In the case of the automatic action, the well-known art such as a motor, is used.
An annular lamp connection section 164 which has a through-hole 164a formed therethrough in the direction of the tube axis of the discharge lamp 12 is provided in the tip of the arm 163c of the Z axial direction drive mechanism 163. By inserting a connection member 164b, for example, a bolt and the like, from the one end side of the lamp connection section 164 into the through-hole 164a of the lamp connection section 164, the lamp holder 12d is connected to a face of the other end of the lamp connection section 164. Since the outer circumference of the mouthpiece 12c provided in the side tube portion 12b of the discharge lamp 12 is covered with the lamp holder 12d, the discharge lamp 12 is fixed to the lamp connection section 164.
In such a discharge lamp 12, while the discharge lamp 12 installed in the casing 11 is turned on, the radiant intensity of the light emitted to the outside of the casing 11 from the light emission window 112a formed in the casing 11 is measured, the position of the discharge lamp 12 is finely adjusted by the X axis drive mechanism 161, the Y axis drive mechanism 162, and the Z axis drive mechanism 163 so that the radiant intensity of the light may become the optimal.